Effect of R(+)α-Lipoic acid on pyruvate metabolism and fatty acid oxidation in rat hepatocytes

The sensitivity of carnitine palmitoyltransferase I to inhibition by 4-hydroxyphenylglyoxylate was decreased markedly in liver mitochondria isolated from either 48 h-starved or streptozotocin-diabetic rats. These treatments of the rat also decreased the sensitivity of fatty acid oxidation by isolated hepatocytes to inhibition by this compound. Furthermore, incubation of hepatocytes prepared from fed rats with N6O2′-dibutyryl cyclic AMP also decreased the sensitivity, whereas incubation of hepatocytes prepared from starved rats with lactate plus pyruvate had the opposite effect on 4-hydroxyphenylglyoxylate inhibition of fatty acid oxidation. The sensitivity of carnitine palmitoyltransferase I of mitochondria to 4-hydroxyphenylglyoxylate increased in a time-dependent manner, as previously reported for malonyl-CoA. Likewise, oleoyl-CoA activated carnitine palmitoyltransferase I in a time-dependent manner and prevented the sensitization by 4-hydroxyphenylglyoxylate. Increased exogenous carnitine caused a moderate increase in fatty acid oxidation by hepatocytes under some conditions and a decreased 4-hydroxyphenylglyoxylate inhibition of fatty acid oxidation at low oleate concentration, without decreasing the difference in 4-hydroxyphenylglyoxylate inhibition between fed- and starved-rat hepatocytes. Time-dependent changes in the conformation of carnitine palmitoyltransferase I or the membrane environment may be involved in differences among nutritional states in 4-hydroxyphenylglyoxylate-sensitivity of carnitine palmitoyltransferase I.

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AMP-activated kinase reciprocally regulates triacylglycerol synthesis and fatty acid oxidation in liver and muscle: evidence that sn-glycerol-3-phosphate acyltransferase is a novel target

Biochemical Journal ◽

10.1042/bj3380783 ◽

1999 ◽

Vol 338 (3) ◽

pp. 783-791 ◽

Cited By ~ 206

Author(s):

Deborah M. MUOIO ◽

Kimberly SEEFELD ◽

Lee A. WITTERS ◽

Rosalind A. COLEMAN

Keyword(s):

Skeletal Muscle ◽

Fatty Acid ◽

Fatty Acid Oxidation ◽

Rat Hepatocytes ◽

C2c12 Myotubes ◽

Acid Oxidation ◽

Dependent Manner ◽

Triacylglycerol Synthesis ◽

Skeletal Muscle Lipid ◽

Novel Target

AMP-activated kinase (AMPK) is activated in response to metabolic stresses that deplete cellular ATP, and in both liver and skeletal muscle, activated AMPK stimulates fatty acid oxidation. To determine whether AMPK might reciprocally regulate glycerolipid synthesis, we studied liver and skeletal-muscle lipid metabolism in the presence of 5-amino-4-imidazolecarboxamide (AICA) riboside, a cell-permeable compound whose phosphorylated metabolite activates AMPK. Adding AICA riboside to cultured rat hepatocytes for 3 h decreased [14C]oleate and [3H]glycerol incorporation into triacylglycerol (TAG) by 50% and 38% respectively, and decreased oleate labelling of diacylglycerol by 60%. In isolated mouse soleus, a highly oxidative muscle, incubation with AICA riboside for 90 min decreased [14C]oleate incorporation into TAG by 37% and increased 14CO2 production by 48%. When insulin was present, [14C]oleate oxidation was 49% lower and [14C]oleate incorporation into TAG was 62% higher than under basal conditions. AICA riboside blocked insulin's antioxidative and lipogenic effects, increasing fatty acid oxidation by 78% and decreasing labelled TAG 43%. Similar results on fatty acid oxidation and acylglycerol synthesis were observed in C2C12 myoblasts, and in differentiated C2C12 myotubes, AICA riboside also inhibited the hydrolysis of intracellular TAG. These data suggest that AICA riboside might inhibit sn-glycerol-3-phosphate acyltransferase (GPAT), which catalyses the committed step in the pathway of glycerolipid biosynthesis. Incubating rat hepatocytes with AICA riboside for both 15 and 30 min decreased mitochondrial GPAT activity 22–34% without affecting microsomal GPAT, diacylglycerol acyltransferase or acyl-CoA synthetase activities. Finally, purified recombinant AMPKα1 and AMPKα2 inhibited hepatic mitochondrial GPAT in a time-and ATP-dependent manner. These data show that AMPK reciprocally regulates acyl-CoA channelling towards β-oxidation and away from glycerolipid biosynthesis, and provide strong evidence that AMPK phosphorylates and inhibits mitochondrial GPAT.

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Estimation of peroxisomal and mitochondrial fatty acid oxidation in rat hepatocytes using tritiated substrates

Biochemical Journal ◽

10.1042/bj2790147 ◽

1991 ◽

Vol 279 (1) ◽

pp. 147-150 ◽

Cited By ~ 14

Author(s):

R Rognstad

Keyword(s):

Fatty Acids ◽

Fatty Acid ◽

Fatty Acid Oxidation ◽

Specific Inhibitor ◽

Rat Hepatocytes ◽

Acid Oxidation ◽

Relative Distribution ◽

Mitochondrial Fatty Acid Oxidation ◽

Mitochondrial Fatty Acid

The pathways of peroxisomal and mitochondrial fatty acid oxidation were monitored with the use of substrates which produce NAD3H. I used as marker substrates: D-[3-3H]3-hydroxybutyrate for mitochondrial NAD3H production, [2-3H]glycerol for cytosolic NAD3H production, and [2-3H]acetate to measure carbon-bound 3H which was also generated by the metabolism of the commercial 9,10-3H-labelled fatty acids. The assumption that peroxisomal NAD3H can be considered to be equivalent to cytosolic NAD3H was supported using a specific inhibitor of mitochondrial fatty acid oxidation. The approach involves determination of the specific yields, and the relative distribution on carbons 4 and 6, of 3H in glucose from the marker substrates and the labelled fatty acids. In hepatocytes from clofibrate-treated rats, the amount of palmitate or oleate oxidation which starts in the peroxisomes is comparable with that which starts in the mitochondria.

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